1. Field of the Invention
The present invention relates to a gas-fired heating unit comprising at least one atmospheric gas burner provided with a mixing chamber and a burner medium covering the mixing chamber, a combustion chamber inside of which the at least one atmospheric gas burner is arranged, a fuel gas/air supply system that has respective inlets for fuel gas and combustion air arranged outside of the combustion chamber on the heating apparatus, and an ignition device having at least one pilot flame and supply pipe for pilot flame gas.
2. Related Art
These types of gas-fired heating units, to which the invention is related, typically include gas-fired water heaters or gas-fired heating apparatuses, like those used for industrial heating and fireplaces in homes, i.e. for space heating.
Gas-fired water heaters are used in many different forms and in many different power stages in different applications both in the private and also the industrial sector.
This sort of gas-fired water heater is used, for example, for preparation of heated service water in industry or of hot water for heating in homes.
A special embodiment of this sort of gas-fired hot water preparing apparatus is the so-called “water heater” marketed in the U.S.A., which typically prepares and stores shower water for workplaces, homes or the like. For example one such “water heater” is described in U.S. Pat. No. 4,953,510, which comprises a thermally insulated storage tank for supplying heated water.
U.S. Pat. No. 5,875,739 A and U.S. Published patent application 2003/0111 023 A1 disclose a further form of a “water heater”, in which a pre-mixing gas burner, a so-called pre-mix burner, is arranged in a nearly completely closed combustion chamber. This gas burner has a mixing chamber, which is covered with a burner medium preferably a burner mat, and a Venturi pipe connected to the mixing chamber below the burner mat, which extends through the wall of the combustion chamber until at an outside surface of the water heater. A nozzle for supplying fuel gas is arranged within the outlet opening of the Venturi. Primary air, which is then mixed further in the mixing chamber with the fuel gas by convection, is drawn in though this outlet opening when fuel gas flows into this Venturi because of gas flow action.
The invention is used in a gas-fired heating apparatus or unit, especially a water heater having a gas burner of the above-described type.
Usually ignition flames, so-called pilot flames, are used for ignition. For this purpose the gas burner has a small pipe of a smaller diameter outside of the mixing chamber, in which fuel gas flows from below and the ignition flame burns with secondary air at the outlet of this small pipe, which is arranged immediately at the edge of the burner mat.
This structure has a comparatively very high NOx emission. Also the ignition of the main burner is comparatively loud, because the ignition and pilot flame “sets” onto the burner mat of the gas burner at the moment of ignition, i.e. spreads out suddenly on it.